Summary
Sodium taurocholate (NaTC), at concentrations below the critical micellar concentration, caused a transient relaxation of isolated guinea-pig ileum smooth muscle strips. The relaxation was not inhibited by previous incubation with either 10 μM ouabain, 0.4 mM d-tubocurarine or 0.5 μM apamin, ruling out the participation of hyperpolarization of the plasma membrane induced by either stimulation of Na+/K+ ATPase or by opening of Ca++-dependent K+ channels. In guinea-pig ileum smooth muscle cultured cells, addition of NaTC (1 mM) stimulated Na+ uptake and Ca++ efflux. The relaxation induced by NaTC was inhibited by 3′, 4′-dichlorobenzamil, a blocker of the Na+/Ca++ exchanger. Preincubation with NaTC, or its addition during the early stage of the tonic response of the ileum to acetylcholine, enhanced that response, whereas a relaxation was observed when NaTC was added at the late stage of the acetylcholine response. In cultured cells, NaTC potentiated the stimulation of Ca2+ influx by acetylcholine. Our results suggest that NaTC acts on the smooth muscle cell membrane causing a stimulation of the Na+/Ca++ exchange mechanism.
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Correspondence to A. C. M. Paiva at the above address
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Romero, F., Frediani-Neto, E., Paiva, T.B. et al. Role of Na+/Ca++ exchange in the relaxant effect of sodium taurocholate on the guinea-pig ileum smooth muscle. Naunyn-Schmiedeberg's Arch Pharmacol 348, 325–331 (1993). https://doi.org/10.1007/BF00169163
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DOI: https://doi.org/10.1007/BF00169163